Correlation of PM10 oxidative potential with ecotoxicological and cytotoxicological indicators

Exposure to atmospheric particulate matter (PM) has detrimental effects on health. These are due to several physical and chemical properties of PM related to their sources and to atmospheric chemical transformations. However, specific mechanisms of toxicity are still not fully understood. In recent years, there has been a growing evidence that oxidative stress is an important mechanism of toxicity; however, when acellular oxidative potential (OP) data are correlated with the outcomes of in vitro (or in vivo) toxicological tests there are contrasting results (Øvrevik, 2019). In this work, an analysis of the correlation among different indicators of PM10 health effects was done, using the acellular Dithiotreitol (DTT) assay to retrieve OPDTT, the Microtox® test on Vibrio fischeri bacterium to assess the ecotoxicological potential, and the in vitro MTT assay on the human cell line A549 to estimate the cytotoxicological potential. The study was carried out on selected PM10 samples collected between 16/09/2017 and 25/12/2017 at the Environmental-Climate Observatory of ISAC-CNR in Lecce (Southern Italy, 40°20’08” N—18°07’028” E, 37 m asl), regional station of the Global Atmosphere Watch (GAW) network, characterized as an urban background site (Lionetto et al., 2019). Water-soluble fraction of PM10 was obtained, using the whole filter, in 10 mL ultrapure water (Milli-Q). The ecotoxicological potential was assessed by the bioluminescence inhibition assay based on the Gram-negative non-pathogenic bacterium Vibrio fischeri (Microtox® test, exposure 30 mins). The cytotoxicological potential was assessed by the MTT assay (based on a colorimetric reaction dependent on mitochondrial respiration of the cells) on the cell line A549 representative of the alveolar type II pneumocytes of the human lung with an exposure of 24h. The OP, was evaluated with the dithiothreitol assay (DTT), a surrogate for cellular antioxidants, which analyses the rate of DTT depletion catalysed by chemical species present in PM10. Results of all assays are presented as net effect (subtracting blank values) and uncertainties are obtained by analysing repeatability. Results show that PM10 and Microtox outcomes were correlated (Pearson 0.67, p<0.05) for nine of the data pairs (one sample out of trend). PM10 and MTT results were correlated (Pearson 0.91, p<0.05) for eight of the data pairs (two samples out of trend). OPDTTV and PM10 were correlated (R 0.91, p<0.05) with no samples out of trend. MTT and Microtox outcomes were not correlated suggesting that the two toxicological indicators are sensitive to different physical-chemical properties of PM10. Intrinsic oxidative potential OPDTTM (DTT activity normalized with PM10 mass) was correlated with mortality observed with MTT test (normalized with PM10 mass), however, it was not correlated with Microtox outcomes. This suggests that acellular OP DTT could be an indicator of cytotoxicological effects of PM on A549 cells.